Helmets for various activities, including sporting activities and work in dangerous environments, often require a shell or protective surface. The range of shapes and sizes of a wearer's head may require a helmet to be made larger or smaller to fit. Furthermore, adjustment may be required depending on the activity, environmental conditions, appearance, or some other factor. In particular, the wearer of a helmet may want to have a tighter or looser fit, depending on circumstances, or may alternatively want to modify the fit, for example during play, or depending on the season, etc.
Adjustable helmets typically include two sections that are moved to change the length of the helmet. Usually, the two sections are slidingly engaged along their sides and an adjustment mechanism is provided on each side to selectively block the relative sliding motion. Other types of helmets require the use of tools to adjust the relative position of the helmet sections.